Reducing the Fault Current and Overvoltage in a Distribution System with an Active Type SFCL Employed PV System

Transcription

1 Reducing the Fault Current and Overvoltage in a Distribution System with an Active Type SFCL Employed PV System M.S.B Subrahmanyam 1 T.Swamy Das 2 1 PG Scholar (EEE), RK College of Engineering, Kethanakonda, Krishna Dt, A.P India 2 Assistant Professor (EEE), RK College of Engineering, Kethanakonda, Krishna Dt, A.P India Abstract- For a power distribution system with distributed generation (DG) units, its fault current and induced overvoltage under abnormal conditions should be taken into account seriously. Inconsideration that applying superconducting fault current limiter (SFCL) may be a feasible solution, in this paper, the effects of a voltage compensation type active SFCL on them are studied through theoretical derivation and simulation. The active SFCL is composed of an air-core superconducting transformer and a PWM converter. The magnetic field in the air-core can be controlled by adjusting the converters output current, and then the active SFCLs equivalent impedance can be regulated for current limitation and possible overvoltage suppression. During the study process, in view of the changes in the locations of the DG units connected to the system, the DG units injection capacities and the fault positions, the active SFCLs current-limiting and overvoltage suppressing characteristics are both simulated in MATLAB. The simulation results show that the active SFCL can play an obvious role in restraining the fault current and overvoltage, and it can contribute to avoiding damage on the relevant distribution equipment and improve the systems safety and reliability. The entire system will be implemented by using PV System also. I. INTRODUCTION Due to increased consumption demand and high cost of natural gas and oil, distributed generation (DG), which generates electricity from many small energy sources, is be- coming one of main components in distribution systems to feed electrical loads [1] [3]. The introduction of DG into a distribution network may bring lots of advantages, such as emergency backup and peak shaving. However, the presence of these sources will lead the distribution network to lose its radial nature, and the fault current level will increase. Besides, when a single-phase grounded fault happens in a distribution system with isolated neutral, over voltages will be induced on the other two health phases, and in consideration of the installation of multiple DG units, the impacts of the induced over voltages on the distribution network s insulation stability and operation safety should be taken into account seriously. Aiming at the mentioned technical problems, applying superconducting fault current limiter (SFCL) may be a feasible solution. For the application of some type of SFCL into a distribution network with DG units, a few works have been carried out, and their research scopes mainly focus on current-limitation and improvement of protection coordination of protective devices [4] [6]. Nevertheless, with regard to using a SFCL for sup- pressing the induced overvoltage, the study about it is relatively less. In view of that the introduction of a SFCL can impact the coefficient of grounding, which is a significant contributor to control the induced overvoltage s amplitude; the change of the coefficient may bring positive effects on restraining overvoltage. Available 120

2 We have proposed voltage compensation type active SFCL in previous work [7], and analyzed the active SFCL s control strategy and its influence on relay protection [8, 9]. In addition, an 800 V/30 a laboratory prototype was made, and its working performances were confirmed well [10]. In this paper, taking the active SFCL as an evaluation object, its effects on the fault current and overvoltage in a distribution network with multiple DG units are studied. In view of the changes in the locations of the DG units connected into the distribution system, the DG units injection capacities and the fault positions, the current- limiting and overvoltagesuppressing characteristics of the active SFCL are investigated in detail. Fig. 1. Single-phase voltage compensation type active SFCL. (a) Circuit structure and (b) equivalent circuit. II. Structure and Principle of the Active SFCL As shown in Fig. 1(a), it denotes the circuit structure of the single-phase voltage compensation type active SFCL, which is composed of an air-core superconducting transformer and a voltage-type PWM converter. Ls1, Ls2 are the self-inductance of two superconducting windings, and Ms i s the mutual inductance. Z1 is the circuit impedance and Z2 is the load impedance. Ld and Cd ar e used for filtering high order harmonics caused by the converter. Since the voltage-type converter s capability of controlling power exchange is implemented by regulating the voltage of AC side, the converter can be thought as a controlled voltage source Up. By neglecting the losses of the transformer, the active SFCL s equivalent circuit is shown in Fig. 1(b). Available 121

3 Fig. 2. Application of the active SFCL in a distribution system with DG units. A. Applying the SFCL into a Distribution Network with DG As shown in Fig. 2, it indicates the application of the active SFCL in a distribution network with multiple DG units, and the buses B-E are the DG units probable installation locations. When a single-phase grounded fault occurs in the feeder line 1 (phase A, k1 point), the SFCL s mode 1 can be automatically triggered, and the fault current s rising rate can be timely controlled. Along with the mode switching, its amplitude can be limited further. In consideration of the SFCL s effects on the induced overvoltage, the qualitative analysis is presented. In normal (no fault) state, the injected current (I2 ) in the secondary winding of the transformer will be controlled to keep a certain value, where the magnetic field in the air-core can be compensated to zero, so the active SFCL will have no influence on the main circuit. When the fault is detected, the injected current will be timely adjusted in amplitude or phase angle, so as to control the superconducting transformer s primary voltage which is in series with the main circuit, and further the fault current can be suppressed to some extent. The aircore superconducting transformer has many merits, such as absence of iron losses and magnetic saturation, and it has more possibility of reduction in size, weight and harmonic than the conventional iron-core superconducting transformer [11], [12]. Compared to the iron-core, the air-core can be more suitable for functioning as a shunt reactor because of the large magnetizing current [13], and it can also be applied in an inductive pulsed power supply to decrease energy loss for larger pulsed current and higher energy transfer efficiency [14], [15]. There is no existence of transformer saturation in the air-core, and using it can ensure the linearity of ZSFCL well. Available 122

4 III.Mtalab/SimulinkResults Fig.3 MATLAB/SIMULINK Circuit Fig.4 Active SFCL s current-limiting performances under different fault locations.

5 Fig.5 Line current waveforms when the three-phase short-circuit occur at k3 point. Fig.6 source voltage, load voltage, injected voltage of the system Fig.7 MATLAB/SIMULINK Circuit with PV Application

6 Fig.8 source voltage, load voltage, injected voltage of the PV system IV. CONCLUSION In this paper, the application of the active SFCL into in a power distribution network with DG units is investigated. For the power frequency overvoltage caused by a single-phase grounded fault, the active SFCL can help to reduce the overvoltage s amplitude and avoid damaging the relevant distribution equipment. The active SFCL can as well suppress the short-circuit current induced by a three-phase grounded fault effectively, and the power system s safety and reliability can be improved. Moreover, along with the decrease of the distance between the fault location and the SFCL s installation position, the current-limiting performance will increase. In recently years, more and more dispersed energy sources, such as wind power and photovoltaic solar power, are installed into distribution systems. And did extension for this system by using PV application.therefore, the study of a coordinated control method for the renewable energy sources and the SFCL becomes very meaningful, and it will be performed in future. REFERENCES [1] S. Conti, Analysis of distribution network protection issues in presence of dispersed generation, Elect. Power Syst. Res., vol. 79, no. 1, pp , Jan [2] A. S. Emhemed, R. M. Tumilty, N. K. Singh, G. M. Burt, and J. R. McDonald, Analysis of transient stability enhancement of LVconnected induction microgenerators by using resistive-type fault current limiters, IEEE Trans. Power Syst., vol. 25, no. 2, pp , May [3] S.-Y. Kim and J.-O. Kim, Reliability evaluation of distribution network with DG considering the reliability of protective devices affected by SFCL, IEEE Trans. Appl. Supercond., vol. 21, no. 5, pp , Oct [4] S. A. A. Shahriari, A. Yazdian, and M. R. Haghifam, Fault current limiter allocation and sizing in distribution system in presence of distributed generation, in Proc. IEEE Power Energy Soc. Gen. Meet., Calgary, AB, Canada, Jul. 2009, pp [5] S. Hemmati and J. Sadeh, Applying superconductive fault current limiter to minimize the impacts of distributed generation on the distribution protection systems, in Proc. Int. Conf. Environ. Electr. Eng., Venice, Italy, May 2012, pp

7 [6] S.-H. Lim, J.-S. Kim, M.-H. Kim, and J.-C. Kim, Improvement of protection coordination of protective devices through application of a SFCL in a power distribution system with a dispersed generation, IEEE Trans. Appl. Supercond., vol. 22, no. 3, p , Jun [7] L. Chen, Y. Tang, J. Shi, and Z. Sun, Simulations and experimental analyses of the active superconducting fault current limiter, Phys. C, vol. 459, no. 1/2, pp , Aug [8] L. Chen, Y. Tang, J. Shi, Z. Li, L. Ren, and S. Cheng, Control strategy for three-phase four-wire PWM converter of integrated voltage compensation type active SFCL, Phys. C, vol. 470, no. 3, pp , Feb [9] L. Chen, Y. J. Tang, J. Shi, L. Ren, M. Song, S. J. Cheng, Y. Hu, and X. S. Chen, Effects of a voltage compensation type active superconducting fault current limiter on distance relay protection, Phys. C, vol. 470, no. 20, pp , Nov [10] J. Wang, L. Zhou, J. Shi, and Y. Tang, Experimental investigation of an active superconducting current controller, IEEE Trans. Appl. Supercond., vol. 21, no. 3, pp , Jun [11] H. Yamaguchi and T. Kataoka, Stability analysis of air-core superconducting power transformer, IEEE Trans. Appl. Supercond., vol. 7, no. 2, pp , Jun [12] H. Yamaguchi, T. Kataoka, H. Matsuoka, T. Mouri, S. Nishikata, and Y. Sato, Magnetic field and electromagnetic force analysis of 3-phase aircore superconducting power transformer, IEEE Trans. Appl. Supercond., vol. 11, no. 1, pp , Mar [13] M. Song, Y. Tang, N. Chen, Z. Li, and Y. Zhou, Theoretical analysis and experiment research of high temperature superconducting aircore transformer, in Proc. Int. Conf. Electr. Mach. Syst., Wuhan, China, Oct. 2008, pp [14] R. Wu, Y. Wang, Z. Yan, W. Luo, and Z. Gui, Design and experimental realization of a new pulsed power supply based on the energy transfer between two capacitors and an HTS air-core pulsed transformer, IEEE Trans. Plasma Sci., vol. 41, no. 4, pp , Apr [15] R. Wu, Y. Wang, Z. Yan, Z. He, and L. Wang, Simulation and experimental investigation of an inductive pulsed power supply based on the head-to-tail series model of an HTS air-core pulsed transformer, IEEE Trans. Appl. Supercond., vol. 23, no. 4, p , Aug [16] S. Chen, W. Wang, and P. Yang, Effects of current-limiting inductor on power frequency overvoltages in transmission line, Power Syst. Technol., vol. 34, no. 3, pp , Mar [17] L. Chen, Y. J. Tang, J. Shi, N. Chen, M. Song, S. J. Cheng, Y. Hu, and X. S. Chen, Influence of a voltage compensation type active superconducting fault current limiter on the transient stability of power system, Phys. C, vol. 469, no , pp , Oct First Author: M.S.B Subrahmanyam, graduate in Electrical and Electronics Engineering (EEE) from Vikas College of engineering and Technology, Krishna dt. He is pursuing his M.Tech from RK College of engineering, kethanakonda, Krishna dt. His Research Interests is Power Systems, Power Electronics. Second Author: T. S w a m y D a s is working as Assistant Professor in Department Of EEE at RK College of engineering, kethanakonda, Krishna dt. Affiliated to JNTUK, Kakinada, A.P, India His Research Interests are Power Systems, Power Electronics, and drives & FACTS devices. Available 126